1. Field of the Invention
The present invention relates to a touch panel used for operating various types of electronic devices.
2. Background Art
In recent years, various types of electronic devices such as a mobile phone and car navigation system, with their higher functionality and diversification proceeding, have been increasingly equipped with a light-transmissive touch panel on the front surface of their display element such as a liquid crystal screen. A user of the device selects each function of the device by pressing the touch panel with a finger, dedicated pen, or the like, while viewing the display on the display element on the back surface through this touch panel. Such a touch panel is demanded that provides reliable operation with high visibility.
A description is made for the conventional touch panel, using FIG. 6.
FIG. 6 is a sectional view of the conventional touch panel. In FIG. 6, upper substrate 51 is film-like and formed with light-transmissive polycarbonate or the like. Lower substrate 52 is light-transmissive as well. A lower surface of upper substrate 51 is formed thereon with light-transmissive upper conductive layer 53 made of a material such as indium tin oxide. A top surface of lower substrate 52 is formed thereon with light-transmissive lower conductive layer 54 made of a material such as indium tin oxide.
Further, a top surface of lower conductive layer 54 is formed thereon with a plurality of dot spacers (not illustrated) made of insulating resin at certain intervals. Additionally, both ends of upper conductive layer 53 are formed thereon with a pair of upper electrodes (not illustrated). Both ends of lower conductive layer 54 are formed thereon with a pair of lower electrodes (not illustrated) orthogonally to the upper electrodes.
Top and lower surfaces of frame-like spacer 55 are coated and formed thereon with an adhesive layer (not illustrated). This adhesive layer bonds respective outer sides of upper substrate 51 and lower substrate 52. In this way, upper conductive layer 53 and lower conductive layer 54 are arranged facing each other with a certain gap provided.
Further, polarizer 56A is made from iodine and dye oriented in polyvinyl alcohol. Top and lower surfaces of polarizer 56A are interposed between and bonded by triacetylcellulose film 56B (hereinafter referred to as “TAC film 56B”) to form polarizing plate 56. Polarizing plate 56 is bonded onto the top surface of upper substrate 51 to compose touch panel 50.
Touch panel 50 composed in this way is arranged on a front surface of a liquid crystal display element or the like (not illustrated) to be attached to an electronic device. Further, the pair of upper electrodes and the pair of lower electrodes are respectively connected to an electronic circuit (not illustrated) of the device.
While display on the liquid crystal display element on a back surface of touch panel 50 being viewed, the top surface of polarizing plate 56 is pressed with a finger, pen, or the like. Consequently, upper substrate 51 deforms along with polarizing plate 56, causing upper conductive layer 53 corresponding to a position having been pressed to contact lower conductive layer 54.
Then, a voltage is applied sequentially to the upper and the lower electrodes from the electronic circuit. The electronic circuit detects a position having been pressed using a voltage ratio between these electrodes, selecting various functions of the device.
Meanwhile, external light such as sunlight and lamplight, emitted from above touch panel 50 transmits through polarizing plate 56. When external light transmits, light waves in direction X and direction Y, orthogonal to direction X, become linearly-polarized light in either of the two directions, owing to polarizing plate 56. Then, this linearly-polarized light enters into upper substrate 51.
The incident light transmitting through upper substrate 51 reflects upward on lower conductive layer 54. However, the amount of the reflected light is reduced roughly by half due to polarization when transmitting through polarizing plate 56. Consequently, a small amount of reflected light emerges from the top surface of polarizing plate 56. That is to say, the liquid crystal display element or the like on the back surface of touch panel 50 with polarizing plate 56 affords higher visibility.
Conventional touch panel 50 is disclosed in Japanese Patent Unexamined Publication No. 2002-297319, for example.